1. Field of the Invention
This invention relates to a switch device for selectively switching a plurality of fixed contacts, and more particularly to a switch device suitable for an electronic device which operates during switching superhigh-speed signals such as, for example, a variable mechanism for a superhigh-speed variable delay line.
2. Description of the Prior Art
A conventional switch device of this kind is constructed as illustrated in the diagram titled "Prior Art".
To be specific, this switch device is constructed by forming a row 5 of a plurality of fixed contacts 3 spaced at a prescribed pitch on a board 1, disposing a conductive plate 7 above the row 5 of fixed contacts, interposing a holder 9 in the shape of a frame between the conductive plate 7 and the row 5 of fixed contacts, and setting a contact spring 11 substantially in the shape of the letter W within the holder 9 in such a manner that a central curved part 13 there of will come into resilient contact with the fixed contacts 3 and outer curved parts 15,15 at the opposite ends thereof will come into contact with the conductive plate 7. The holder 9 has its part thrust out of a slit 17 formed in the conductive plate 7 in the direction of the row 5 of fixed contacts and has a knob 19 attached to the thrust part, so that the holder 9 is supported by keeping the conductive plate 7 nipped between itself and the knob 19. In the contact spring 11, the end ports from the outer curved parts 15,15 to opposite free ends 21,21 are short and these free ends 21,21 are adapted to come into contact with inner walls 23,23 of the holder 9.
In the switch device so constructed, when the holder 9 is moved by a push given to the knob 19, one of the inner walls 23,23 of the holder 9 pushes one of the free ends 21,21 of the contact spring 11 and, consequently, the contact spring 11 is moved in conjunction with the holder 9. Any fixed contact 3 selected from the row 5 of fixed contacts, therefore, can be connected to the conductive plate 7 with the contact spring 11 serving as a movable contact.
When a superhigh-frequency signal having a rise time of not more than 1 ns is applied to the conductive plate 7, this signal flows to the fixed contact 3 through the two paths between the curved parts 15-13 and between the curved parts 15-13 of the contact spring 11. Since this contact spring 11 has a low inductance in the sections thereof used for the flow of the signal, this switch device is believed to suit the switching of superhigh-speed signals.
During the course of quantity production of switch devices of the aforementioned construction, however, a gap G between the row 5 of fixed contacts and the conductive plate 7 is liable to disperse from one product to another, and the shape of curved of the contact spring 11 tends to vary from one switch device to another. When the gap G is dispersed, the position and the angle which the free and 21 of the contact spring 11 assumes and forms on contact with the inner wall 23 of the holder 9 vary and the sensation from the manipulation of the knob 19 varies from one switch device to another. Thus, the reliability of the switch device of this conventional construction is jeopardized by such possibility of quality dispersion and is degraded high yield in quantity production.
When the contact spring 11 moves on while alternately repeating single contact with one fixed contact 3 and dual contact with two adjacent fixed contacts 3 in consequence of the motion of the knob 19, the curved shape of the contact spring 11 similarly repeats variation for each change from single contact to dual contact. Thus, the position and the angle which the free end 21 of the contact spring 11 assumes and forms on contact with the inner wall 23 vary for each change from single contact to dual contact, with the result that the slidability of the free end 21 is degraded, and the inferior sensation of the manipulation of the knob 19 is exacerbated all the more. Moreover, since the pressure of contact which the contact spring 11 exerts upon the fixed contacts 3 is alternately increased and decreased both greatly, the surfaces of the fixed contacts 3 and the contact spring 11 are worn out quickly so much as to impair the stability of contact resistance and degrade the reliability of performance.
For the solution of these drawbacks, it is sufficient to improve the accuracy of component and the accuracy of work of assembly and minimize the dispersion in the gap G between the row 5 of fixed contacts and the conductive plate 7. The efforts directed to the fulfilment of the requirement, however, prove impracticable because they entail a rise of the production cost and a fall of the efficiency of production.